1. Field of the Invention
The invention relates to an optical disc identification method and more particularly, to a method used in an optical disc reproduction system for identifying the type of an optical disc.
2. Description of the Prior Art
Optical storage media is a commonly used media for storing large amounts of data. Compact discs (CD), digital versatile discs (DVD), and super audio compact disc (SACD) are examples of optical storage media. Many kinds of optical disc reproduction systems can be found on the market. One main feature is an optical disc reproduction system always combines the ability of reading information from a CD and the ability of reading information from a DVD (some systems even combine the ability of writing information onto a CD or a DVD). In order for an optical disc reproduction system with combined reading ability to identify the type of an optical disc, an effective optical disc identification method must be used.
Please refer to FIG. 1 where a block diagram of an optical disc reproduction system is illustrated. The optical disc reproduction system 100 comprises a pickup 120. The pickup 120 comprises a CD light source, a DVD light source (neither are shown in this figure), and an object lens 130. A focus driving voltage (FOD) can drive the object lens 130 up or down (perpendicularly to the surface of the optical disc 190) in order to move the focus location of the CD light source or the DVD light source. The pickup 120 further comprises a light detector (also not shown in this figure) that can detect a light signal reflected back from the optical disc 190. A signal processing unit 140 processes the signal detected by the light detector into other kinds of signals or information that is needed.
Normally, the signal processing unit 140 generates a focus error signal (FE signal) and a radio frequency signal (RF signal). Different kinds of optical discs 190 generate different characteristics for the FE signal and RF signal.
Yang et al. in United States Patent Application Publication 2003/0039189 discloses a method for identifying the type of an optical disc. Generally speaking, the method measures the amplitude (a maximum subtracted by a minimum) of the FE signal generated by the signal processing unit 140 while the CD light source on the pickup 120 is turned on, and the object lens 130 is moving up and down. If the amplitude is larger than a predetermined threshold, then the optical disc 190 will be identified as a CD type optical disc (such as CD-ROM, CD+−RW); if the amplitude is smaller than the threshold, then the optical disc 190 will be identified as a DVD type optical disc (such as single-layer DVD-ROM, dual-layer DVD).
However, the optical disc reproduction system 100 usually has to deal with many kinds of optical discs, some of which may be of bad quality. Sometimes, the above-mentioned optical disc identification method using only one judging condition (the amplitude) wrongly identifies the disc type of an optical disc of bad quality. If a DVD-type optical disc is mistakenly identified by the optical disc reproduction system 100 as a CD-type optical disc or vice versa, the optical disc reproduction system 100 may not be able to read information stored in the optical disc correctly, or worse yet, the whole system may even break-down.